This invention relates to brushes for dynamoelectric machines and more particularly to a method for making multi-element brushes having thousands of hair-like conductive fibers.
Advanced current collection research is being conducted to improve brush current density from the present level of 1.55 milliamps per square meter (1,000 amps per square inch) to 7.75 milliamps per square meter (5,000 amps per square inch). The main thrust of this research is to achieve very high density current collection systems, which will lead to new compact dynamoelectric machines for high mobility systems application.
Presently when utilizing solid body type brushes, due to their hardness, elastic and plastic deformation, which occurs in both bodies, only 10 to 50 contact points are made between the slipring and the collector surface. One approach to improve the number of contact points is the multi-element brush in which a large number of essentially independent sub-units, the fibers, make contact with the slipring or current collector. The multiplicity of independent contact members insures a multiplicity of contact points.
The problem in fabricating a brush consisting of thousands of metal, metal-plated graphite or carbon fibers generally having a diameter of 8 to 10 microns is joining together one end of the brush in good electrical contact and in having the other end loosely packed for contacting the collector surface. The hair-like fibers are difficult to handle and to fabricate a reproducible brush consistent in fibers per unit area, fiber flexibility and also producing a joint on the other end of low resistance. The initial procedure for producing multi-fiber brushes was to tie a bundle of fibers together and soft solder one end to a piece of copper; this procedure will not produce consistent fiber brushes.